The present invention relates to an apparatus for processing the outputs of a two-dimensional planar array of spaced apart receiving elements where the receiving elements are grouped in spaced apart rows. This processing enables two-dimensional imaging of a far field radiating source with respect to the planar array.
Beamforming can be accomplished with a linear array of receiving elements, such as passive hydrophones. Beamforming is accomplished by providing an appropriate delay or phase shift to the outputs from the receiving elements so as to obtain a maximum summation thereof. This is called steering the beam, and will provide information on the direction of a target with respect to the linear array of listening elements. A basic patent on the delay line technique for beamforming is illustrated in the patent to G. W. Dewitz, U.S. Pat. No. 3,037,185.
Two dimensional imaging is in essence simultaneous beamforming in two directions, these directions normally being perpendicular with respect to one another. With such an arrangement the receiving elements must also be arranged in a two dimensional fashion, such as a plurality of rows of receiving elements within a common plane. Two dimensional imaging provides additional information over simple linear array beamforming. Simple linear array beamforming does not provide the exact direction to the sound source, but in contrast only provides a planar direction thereto. Two dimensional imaging provides information which indicates the exact direction of the radiating source from the planar array. The only information lacking in the two dimensional array, in regard to the exact location of the radiating source, is the range to the radiating source from the planar array.
Numerous imaging systems exist for the various segments of the electromagnetic or acoustic spectrum. Prior art imaging systems utilized in the microwave and millimeter region are usually not suitable for real time imaging. Further, these systems typically involve cumbersome mechanical scanning of aperture antennas. Another approach is the existing phased array method. Unfortunately, these methods normally require extensive numerical calculations or complex filtering and therefore are quite costly. In general, the prior art imaging systems are bulky, expensive to construct, and many do not provide real time information.